1. Field of the Invention
The present invention relates to a control valve for controlling a flow rate of fluid (liquid or gas) to be constant, and especially relates to a flow control valve for controlling a constant flow rate by absorbing not only pressure fluctuations on the primary side (inflow side) but also load fluctuations on the secondary side (outflow side).
2. Description of the Related Art
The inventor of the present invention has proposed a fluid control valve using diaphragms, in Japanese Unexamined Patent Publication (Kokai) No. 6-295209, in which the flow rate on the secondary side (outflow side) can be kept constant in response to the pressure fluctuation on the primary side (inflow side). The invention was patented as Japanese Patent No. 2671183.
The fluid control valve 100 of the prior invention, shown in FIG. 3, is comprised of a body 110 having an inflow part 111 and an outflow part 112, and a valve body 120 having a valve part 121, a first diaphragm part 122 and a second diaphragm part 123. The chamber of the body 110 is divided, by the first diaphragm part 122 and the second diaphragm part 123, into a first pressure chamber 131, a valve chamber 130, and a second pressure chamber 132. The first pressure chamber 131 and the second pressure chamber 132 are always under constant pressure so as to exert inward pressure on the first diaphragm part 122 and the second diaphragm part 123 from the outside. Numbers 136 and 137 designate passages of pressurized gas.
According to the fluid control valve 100 of the prior invention, the pressure fluctuation on the inflow part 111 side (primary side) produces a fluctuation of the outward pressure which acts on the first and the second diaphragm parts 122 and 123 that are continuously subject to constant inward pressure. Consequently a displacement of the valve body 120 occurs to keep a balance between the constant inward force and the fluctuating outward pressure on the primary side. The displacement of the valve body 120 causes the valve part 121 to move, so that the valve opening changes to thereby control the flow rate.
The prior invention has a great advantage that a quick response to an instant pressure variation or pulsation to which conventional mechanical or electrical means could not quickly respond can be provided, using a valve body having two diaphragm parts. Also, since the structure is simple, installation and maintenance thereof can be advantageously facilitated.
However, the prior invention does not have a function to respond to the load fluctuation on the outflow side, i. e., the secondary side. Accordingly, it is not responsive, for example, to an influence by mixing with another fluid on the secondary side, or a load fluctuation caused by a change in the viscosity of the fluid, due to a temperature change.